A paper on the genetic condition in Connemara ponies known as Hoof Wall Separation Disease has been published in the latest issue of the peer-reviewed journal, PLOS Genetics.
The inherited disease manifests itself as separation of the dorsal hoof wall along the weight-bearing surface of the hoof during the first year of life.
The disease is a genetic autosomal recessive condition. Two carrier parents being bred with each other result in a one in four chance of the foal being afflicted with the distressing disease. It was announced last September that a genetic test for the disease was commercially available.
Researchers in the Bannasch Laboratory at the University of California, Davis, led the research and identified the genetic basis of the disease, which is characterized by a hoof wall that easily breaks and cracks, and a normal-looking coronary band.
The scientists, led by Dr Carrie Finno, carried out their work on behalf of the Connemara Pony Research Group. It began in November 2011.
The very existence of the disease and that it was of genetic origin had, until confirmation of its cause, been questioned by many people throughout the Connemara Pony breeding world.
Those who had not seen or personally experienced the condition were reluctant to accept that such a serious problem could exist within the breed.
It has been stressed that carriers, who can be bred safely to non-carriers, must be retained in the breeding herd in order to help maintain diversity within the breed and to maintain other positive attributes.
The condition has been identified in a range of countries, in both local and imported stock – not one country nor one bloodline.
The paper, entitled “SERPINB11 Frameshift Variant Associated with Novel Hoof Specific Phenotype in Connemara Ponies”, outlines evidence that points to a clear role of the SERPINB11 gene in maintaining hoof wall structure, with a recessive variant of the gene identified as causing the disease.
The paper describes what it says is the first genetic variant associated specifically with the hoof wall. The SERPINB11 variant behind the disease does not appear to involve or affect any other organs in which the gene is expressed.
The researchers based their findings on work with 423 Connemara ponies. Among them, they found 31 affected ponies, all homozygous for the SERPINB11 gene responsible for the disease – that is, they inherited the gene from both parents.
The severity of the disease in these 31 ponies ranged from mild, where the pony was able to be maintained with frequent hoof trimming and shoeing, to severe.
Within the 423-Connemara ponies, 18.7 percent (a total of 96 ponies) were carriers – that is, they had inherited the recessive gene from one of their parents. All were unaffected by the disease.
Within a 324-pony subset of individuals unrelated to the affected animals, carrier frequency for the variant was found to be 14.8 percent.
The researchers involved in the study were Carrie Finno, Carlynn Stevens, Danika Bannasch, Amy Young, Verena Affolter and Nikhil Joshi, all from the University of California, Davis; and Sheila Ramsay, from New Zealand’s Massey University.
The study in PLOS Genetics can be read in full here.
Earlier reports on Connemara Hoof Wall Disease: